摘要
本文首次测得江西弋阳中元古界铁沙街组石英角斑岩SHRIMP锆石U-Pb年龄为1154±5 Ma。测定发现铁沙街组石英角斑岩和流纹岩高SiO_2(73.53%~81.11%),低CaO(0.06%~0.11%)、Na_2O(0.05%~2.77%),K_2O为2.16%~6.43%和Al_2O_3为11.06%~13.96%;在Zr/TiO_2—Nh/Y微量元素分类图解上绝大多数样品落于碱性流纹岩区域;在SiO_2—FeO/MgO图解中绝大多数样品位于钙碱性岩石系列区域;稀土总量(ΣREE)为182.48×10^(-6)~818.82×10^(-6),轻稀土较富集,铕明显负异常(δEu=0.20~O.45);在原始地幔标准化图解中,表现出亏损大离子亲石元素(Ba、Sr、Ti、P)和富集高场强元素(Nb、Ta、La、Ce、Zr、Hf、Sm)。铁沙街组石英角斑岩和流纹岩的锆石的ε_(Hf)(t)值分别为-6.1~5.3和-2.3~4.8,两阶段Hf模式年龄分别为1653~2380 Ma和1675~2132 Ma。锆石Hf同位素特征显示铁沙街组石英角斑岩、流纹岩的成因主要为岩石圈拆沉,深部地幔物质上涌,并由此造成的古元古代晚期下地壳物质的部分熔融。综上认为,铁沙街组石英角斑岩和流纹岩形成于中元古界后造山阶段的板内环境,可能与华夏陆块板内裂谷减薄开裂阶段的地幔物质上涌有关。
Zircon SHRIMP U-Pb dating of quartz keratophyre is first time to report from the Tieshajie Formaion （1 154 ±5 Ma）,Mesoproterozoic.The quartz keratophyre and rhyolite from the Tieshajie Formaion,with high SiO2 （73.53%~81.11%）,low CaO （0.06%~0.11%）,low Na2O （0.05%~2.77%）,Al2O3 （11.06%~13. 96%）,and K2O （2.16%~6.43%）.The quartz keratophyre and rhyolite belongs to alkali rhyolite rock series showed in the classification diagram of Zr/TiO2—Nb/Y and calc-alkaline rock series showed in the SiO2— FeO/MgO diagram.The rocks have higher REE contents （182.48 ×10 -6 ~818.82 ×10 -6）with relative enrichment of LREE and negative Eu anomaly （δEu=0.20~0.45）.The primitive mantle normalized trace element patterns are characterized by the depletion of the LILE （Ba,Sr,Ti,P）and enrichment of the HFSE （Nb,Ta,La,Ce,Zr, Hf,Sm）.TheεHf（t）values and two-staged Hf model ages of the quartz keratophyre and rhyolite from the Tieshajie Formaion are -6.1 ~5.3 and -2.3 ~4.8,1653 ~2380 Ma and 1675 ~2132 Ma.Zircon Hf isotopes characteristic shows that,the quartz keratophyre and rhyolite from the Tieshajie Formaion are products from the lithosphere delamination and mantle material upwelling,and partial melting of late paleoproterozoic crust materials. Synthetical analyze,the Tieshajie Formaion formed in a continental intraplate setting,postorogenic stage.It may be formed in cracking stage of intraplate rift of the Cathaysia,and products of mantle material upwelling.
出处
《地质论评》
CAS
CSCD
北大核心
2015年第1期65-78,共14页
Geological Review
基金
中国地质调查局项目(编号121201011120131和1212011120117)
全国油气基础地质研究与编图项目(编号2011ZX05043-005)的成果
作者简介
张恒，男，1985年生。博士研究生。研究方向为前寒武纪沉积和大地构造学。Emml：heng0520@126．com。
通讯作者：高林志，男，1955年生。研究员。主要从事生物地层、层序地层、灾变事件地层研究。Email：gaolzh@cags．ac．cn。
